A trusted login procedure can also be referred to as an auto login procedure between two services. In one example, a user can log into a website of the first service to perform an online transaction. The login can be performed using security credentials such as a username, a password, or a combination thereof. To complete the online transaction, the user may be redirected to a website of a second service to process the online transaction. In some cases, the user can complete the processing without using the security credentials again. In other words, the website of the second service can be configured to trust a user who has already logged into the website of the first service for the online transaction. Examples of the website of the first service can include an online shopping website, a website providing organized activities, and a website providing personal or enterprise services. Examples of the websites of the second service can include a payment website that is used to enter payment information to complete the online shopping and a registration website that is used to register for a specific activity.